Filter By Variable Captured From Input Box

I have a Workbook containing a list of records. I'd like to create some code to

1) Get the user to input their initials when the workbook opens, and capture the response
2) Clear any filters currently applied
3) Apply filters to a non-continous range of columns
4) Apply the input response as the criteria to one of the columns, and 'blanks' to another 2 columns

Private Sub Workbook_Open()
Static varUser As String
'sets varUser variable as String & stores it
varUser = InputBox(Prompt:="Enter Intials (leave blank to view all)", Title:="Login")
'Activates input box to capture value
Dim ContractsSheet As Range
Set ContractsSheet = Worksheets("Contracts").Range("A1:AA999")
ContractsSheet.EntireRow.Hidden = False....................